Flexibility of DME reactor. The flexibility of the DME reactor has been identified as a crucial system parameter for cost reduction (cf. Section 3.2.5). In this section we vary the flexibility of the DME reactor. We identify the influence on costs, storage sizes, utilization rate and curtailment amounts as a function of the minimum load of the DME reactor. We observe a strong cost reduction potential if the DME reactor could be operated flexibly in a dynamic load change of 40 – 100% (cf. Figure 24). In the base case (that is 80% minimum load constraint) the levelized costs are 3.43 €/kg. A flexibility enhancement up to 40% minimum load leads to levelized costs below 3.2 €/kg. However, it is well known that a dynamic operation of distillation columns is very challenging. The technical and economic feasibility of a flexible DME reactor is not part of this report. Figure 24: Levelized cost of DME as a function of the minimum load of the DME reactor The minimum load constraint influences the optimal system layout, in particular the size of the storages. In general, the higher the flexibility the more important the battery storage becomes and the less important the hydrogen storage becomes. This can be explained by the fact that enhanced flexibility enables the DME reactor to follow the load of the electrolyzer, thus an intermediate hydrogen storage becomes more and more obsolete. Potentially, the complexity of the whole process can be decreased significantly with an increased flexibility of the DME reactor. Thus, it does not only have an impact on cost reduction but also increases the degrees of freedom in the system design. The storage sizes as a function of the minimum load constraint of the DME reactor are shown in Figure 25. Figure 25: Storage sizes (for battery and hydrogen) as a function of the minimum load of the DME reactor Curtailment appears in times of high electricity generation combined with a fully utilized system and full storages. The minimum load constraint also impacts the curtailed amounts of electricity. In particular, curtailment can be reduced drastically for a minimum load below 50% (cf. Figure 26). The average load of the electrolyzer is hardly affected by the minimum load constraint. It is fairly constant at a load level around 70%. However, a fully flexible DME reactor results in an average load of such of 75%. In other words, DME and electrolyzer excess capacity is required to deal with the intermittent character of renewable generation.
